System and method for gesture based control system

ABSTRACT

The system provides a gestural interface to various visually presented elements, presented on a display screen or screens. A gestural vocabulary includes ‘instantaneous’ commands, in which forming one or both hands into the appropriate ‘pose’ results in an immediate, one-time action; and ‘spatial’ commands, in which the operator either refers directly to elements on the screen by way of literal ‘pointing’ gestures or performs navigational maneuvers by way of relative or “offset” gestures. The system contemplates the ability to identify the users hands in the form of a glove or gloves with certain indicia provided thereon, or any suitable means for providing recognizable indicia on a user&#39;s hands or body parts. A system of cameras can detect the position, orientation, and movement of the user&#39;s hands and translate that information into executable commands.

This patent application claims priority to U.S. Provisional PatentApplication 60/651,290 filed Feb. 8, 2005 entitled “Gesture BasedControl System”, which is incorporated herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of computer system in general and inparticular to a system and method for a gesture based control system.

2. Background

A user may enter commands and interact with a computer system bymanipulating data or images in a window on a display, or by selectingoperations from a menu associated with the window or an associatedprogram, using input devices such as a mouse, keyboard, joystick,cross-key, or the like. Such input devices may also operate as positiontranslating devices, which can be used to position a graphical,on-screen pointer, such as a cursor. A cursor functions, for example, toindicate a character to be revised or to indicate a position where datais to be entered or an operation is to be performed. A cursor, in someform or appearance, is typically present on the computer display.Manipulation of an input device by a user will result in a correspondingmovement of the cursor. Thus, for example, movement of a mouse or otherinput device results in movement of the cursor in the same direction.

A cursor may have different appearances depending on its function andthe state of the computer system. For example, when positioned in a textfield on a computer display, the cursor may have the appearance of an“I-beam”, or a blinking vertical line. The position of the cursor in atext field indicates the location of the next character that will beentered by the user, typically via a keyboard. The cursor may have otherappearances depending on its function. In a drawing or painting program,the cursor may be represented as a paint brush, pencil, eraser, bucket,or other graphic form.

The cursor may also take the shape of an arrow or pointer whenpositioned over user-selectable operations or when it is used to selectgraphical elements, such as windows. To select and activate a desiredoperation with the cursor, it may be positioned over a graphical or textrepresentation of the operation. A button located on a mouse inputdevice may be depressed and/or released to effectuate the operation. Theuser is notified of the acceptance of the operation for execution byvisual feedback, usually in the form of some change in an image on thecomputer's display. One or more of the programs in use typicallygenerates this visual response. These programs generate drawing commandsto update the display images in response to the selected operations.

A disadvantage of prior art systems is that the input device is oftenjust that, a device. The user is required to have a wired or wirelessmouse or other input device and to use that device to manage selection,position translation, activation, and other input functions. Often theuse of these physical devices is not natural or intuitive. Anotherdisadvantage is the need to go through certain steps to change thecontext of the input device so that different functions may beperformed.

With the popularity of very large displays, further disadvantages ofprior art input devices and systems become apparent. When using a mousefor example, to attempt to translate the position of a cursor across alarge display, the user must often lift the mouse and replace it on themouse surface to enable the user to drag the cursor across even aportion of a large display. This is a wasted an unnatural motion.

There have been some prior art attempts to provide a solution to theseproblems. One prior art solution is the use of gloves on the users hand.These gloves deign to turn the users hand or hands into input devices.In one embodiment, an input glove is hard wired to a computer system.This solution has the disadvantage of literally tying the user to thespot, requiring a nearness to the computer system and a restriction onrange of motion. In other cases, the gloves are wireless. However, suchwireless implementations require an independent power supply for theglove. When the power supply needs to be recharged, the gloves may notbe used.

SUMMARY OF THE INVENTION

The system provides a gestural interface to various visually presentedelements, presented on a display screen or screens. The operator of thesystem navigates and manipulates these elements by issuing a continuousstream of ‘gestural commands’ using the operators hands in oneembodiment. In other embodiments, a user's head, feet, arms, legs, orthe whole user may be used to provide the navigation and control. Thegestural vocabulary includes ‘instantaneous’ commands, in which formingone or both hands into the appropriate ‘pose’ results in an immediate,one-time action; and ‘spatial’ commands, in which the operator eitherrefers directly to elements on the screen by way of literal ‘pointing’gestures or performs navigational maneuvers by way of relative or“offset” gestures. In addition to pointing gestures, which are used forabsolute or direct spatial gesturing, the invention may also recognizeanother category of relative spatial navigation gestures in an XYZspace. This category of actions is sometimes referred to as XYZtechniques. By maintaining a high frame rate, by guaranteeing a nearlyimperceptible lag in the interpretation of operator gestures, and byemploying both carefully designed spatial metaphors and readily evident‘direct manipulation’ mechanism, the system provides a vivid ‘cognitivecoupling’ between the operator and the information & processes beingrepresented. The system contemplates the ability to identify the user'shands. This system of identification may be in the form of a glove orgloves with certain indicia provided thereon, or any suitable means forproviding recognizable indicia on a user's hands. A system of camerascan detect the position, orientation, and movement of the user's handsand translate that information into executable commands.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an embodiment of the system of the invention.

FIG. 2 is a diagram of an embodiment of marking tags of the invention.

FIG. 3 is a diagram of poses in a gesture vocabulary in an embodiment ofthe invention.

FIG. 4 is a diagram of orientation in a gesture vocabulary in anembodiment of the invention.

FIG. 5 is a diagram of two hand combinations in a gesture vocabulary inan embodiment of the invention.

FIG. 6 is a diagram of orientation blends in a gesture vocabulary in anembodiment of the invention.

FIG. 7 is a flow diagram illustrating the operation an embodiment of thesystem of the invention.

FIG. 8 is an example of commands in an embodiment of the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A system and method for a gesture based control system is described. Inthe following description, a number of features are described in detailin order to provide a more thorough understanding of the invention. Itis apparent that the invention may be practiced without out thesespecific details. In other cases, well known features have not beendescribed in detail.

System

A block diagram of an embodiment of the invention is illustrated inFIG. 1. A user locates his hands 101 and 102 in the viewing area of anarray of cameras 104A-104D. The cameras detect location, orientation,and movement of the fingers and hands 101 and 102 and generate outputsignals to pre-processor 105. Pre-processor 105 translates the cameraoutput into a gesture signal that is provided to the computer processingunit 107 of the system. The computer 107 uses the input information togenerate a command to control one or more on screen cursors and providesvideo output to display 103.

Although the system is shown with a single user's hands as input, theinvention may also be implemented using multiple users. In addition,instead of or in addition to hands, the system may track any part orparts of a user's body, including head, feet, legs, arms, elbows, knees,and the like.

In the embodiment shown, four cameras are used to detect the location,orientation, and movement of the user's hands 101 and 102. It should beunderstood that the invention may be used with more or fewer cameraswithout departing from the scope or spirit of the invention. Inaddition, although the cameras are disposed symmetrically in the exampleembodiment, there is no requirement of such symmetry in the invention.Any number or positioning of cameras that permits the location,orientation, and movement of the user's hands may be used in theinvention.

In one embodiment of the invention, the cameras used are motion capturecameras capable of capturing grey-scale images. In one embodiment, thecameras used are those manufactured by Vicon, such as the Vicon MX40camera. This camera includes on-camera processing and is capable ofimage capture at 1000 frames per second. A motion capture camera iscapable of detecting and locating markers.

In the embodiment described, the cameras are used for optical detection.In other embodiments, the cameras or other detectors may be used forelectromagnetic, magnetostatic, RFID, or any other suitable type ofdetection.

Pre-processor 105 is used to generate three dimensional space pointreconstruction and skeletal point labeling. The gesture translator 106is used to convert the 3D spatial information and marker motioninformation into a command language that can be interpreted by acomputer processor to update the location, shape, and action of a cursoron a display. In an alternate embodiment of the invention, thepre-processor 105 and gesture translator 106 can be combined into asingle device.

Computer 107 may be any general purpose computer such as manufactured byApple, Dell, or any other suitable manufacturer. The computer 107 runsapplications and provides display output. Cursor information that wouldotherwise come from a mouse or other prior art input device now comesfrom the gesture system.

Marker Tags

The invention contemplates the use of marker tags on one or more fingersof the user so that the system can locate the hands of the user,identify whether it is viewing a left or right hand, and which fingersare visible. This permits the system to detect the location,orientation, and movement of the users hands. This information allows anumber of gestures to be recognized by the system and used as commandsby the user.

The marker tags in one embodiment are physical tags comprising asubstrate (appropriate in the present embodiment for affixing to variouslocations on a human hand) and discrete markers arranged on thesubstrate's surface in unique identifying patterns.

The markers and the associated external sensing system may operate inany domain (optical, electromagnetic, magnetostatic, etc.) that allowsthe accurate, precise, and rapid and continuous acquisition of theirthree-space position. The markers themselves may operate either actively(e.g. by emitting structured electromagnetic pulses) or passively (e.g.by being optically retroreflective, as in the present embodiment).

At each frame of acquisition, the detection system receives theaggregate ‘cloud’ of recovered three-space locations comprising allmarkers from tags presently in the instrumented workspace volume (withinthe visible range of the cameras or other detectors). The markers oneach tag are of sufficient multiplicity and are arranged in uniquepatterns such that the detection system can perform the following tasks:(1) segmentation, in which each recovered marker position is assigned toone and only one subcollection of points that form a single tag; (2)labelling, in which each segmented subcollection of points is identifiedas a particular tag; (3) location, in which the three-space position ofthe identified tag is recovered; and (4) orientation, in which thethree-space orientation of the identified tag is recovered. Tasks (1)and (2) are made possible through the specific nature of themarker-patterns, as described below and as illustrated in one embodimentin FIG. 2.

The markers on the tags in one embodiment are affixed at a subset ofregular grid locations. This underlying grid may, as in the presentembodiment, be of the traditional Cartesian sort; or may instead be someother regular plane tessellation (a triangular/hexagonal tilingarrangement, for example). The scale and spacing of the grid isestablished with respect to the known spatial resolution of themarker-sensing system, so that adjacent grid locations are not likely tobe confused. Selection of marker patterns for all tags should satisfythe following constraint: no tag's pattern shall coincide with that ofany other tag's pattern through any combination of rotation,translation, or mirroring. The multiplicity and arrangement of markersmay further be chosen so that loss (or occlusion) of some specifiednumber of component markers is tolerated: After any arbitrarytransformation, it should still be unlikely to confuse the compromisedmodule with any other.

Referring now to FIG. 2, a number of tags 201A-201E (left hand) and202A-202E (right hand) are shown. Each tag is rectangular and consistsin this embodiment of a 5×7 grid array. The rectangular shape is chosenas an aid in determining orientation of the tag and to reduce thelikelihood of mirror duplicates. In the embodiment shown, there are tagsfor each finger on each hand. In some embodiments, it may be adequate touse one, two, three, or four tags per hand. Each tag has a border of adifferent grey-scale or color shade. Within this border is a 3×5 gridarray. Markers (represented by the black dots of FIG. 2) are disposed atcertain points in the grid array to provide information.

Qualifying information may be encoded in the tags' marker patternsthrough segmentation of each pattern into ‘common’ and ‘unique’subpatterns. For example, the present embodiment specifies two possible‘border patterns’, distributions of markers about a rectangularboundary. A ‘family’ of tags is thus established—the tags intended forthe left hand might thus all use the same border pattern as shown intags 201A-201E while those attached to the right hand's fingers could beassigned a different pattern as shown in tags 202A-202E. Thissub-pattern is chosen so that in all orientations of the tags, the leftpattern can be distinguished from the right pattern. In the exampleillustrated, the left hand pattern includes a marker in each corner andon marker in a second from corner grid location. The right hand patternhas markers in only two corners and two markers in non corner gridlocations. An inspection of the pattern reveals that as long as anythree of the four markers are visible, the left hand pattern can bepositively distinguished from the left hand pattern. In one embodiment,the color or shade of the border can also be used as an indicator ofhandedness.

Each tag must of course still employ a unique interior pattern, themarkers distributed within its family's common border. In the embodimentshown, it has been found that two markers in the interior grid array aresufficient to uniquely identify each of the ten fingers with noduplication due to rotation or orientation of the fingers. Even if oneof the markers is occluded, the combination of the pattern and thehandedness of the tag yields a unique identifier.

In the present embodiment, the grid locations are visually present onthe rigid substrate as an aid to the (manual) task of affixing eachretroreflective marker at its intended location. These grids and theintended marker locations are literally printed via color inkjet printeronto the substrate, which here is a sheet of (initially) flexible‘shrink-film’. Each module is cut from the sheet and then oven-baked,during which thermal treatment each module undergoes a precise andrepeatable shrinkage. For a brief interval following this procedure, thecooling tag may be shaped slightly—to follow the longitudinal curve of afinger, for example; thereafter, the substrate is suitably rigid, andmarkers may be affixed at the indicated grid points.

In one embodiment, the markers themselves are three dimensional, such assmall reflective spheres affixed to the substrate via adhesive or someother appropriate means. The three dimensionality of the markers can bean aid in detection and location over two dimensional markers. Howevereither can be used without departing from the spirit and scope of thepresent invention.

At present, tags are affixed via Velcro or other appropriate means to aglove worn by the operator or are alternately affixed directly to theoperator's fingers using a mild double-stick tape. In a thirdembodiment, it is possible to dispense altogether with the rigidsubstrate and affix—or ‘paint’—individual markers directly onto theoperator's fingers and hands.

Gesture Vocabulary

The invention contemplates a gesture vocabulary consisting of handposes, orientation, hand combinations, and orientation blends. Anotation language is also implemented for designing and communicatingposes and gestures in the gesture vocabulary of the invention. Thegesture vocabulary is a system for representing instantaneous ‘posestates’ of kinematic linkages in compact textual form. The linkages inquestion may be biological (a human hand, for example; or an entirehuman body; or a grasshopper leg; or the articulated spine of a lemur)or may instead be nonbiological (e.g. a robotic arm). In any case, thelinkage may be simple (the spine) or branching (the hand). The gesturevocabulary system of the invention establishes for any specific linkagea constant length string; the aggregate of the specific ASCII charactersoccupying the string's ‘character locations’ is then a uniquedescription of the instantaneous state, or ‘pose’, of the linkage.

Hand Poses

FIG. 3 illustrates hand poses in an embodiment of a gesture vocabularyusing the invention. The invention supposes that each of the fivefingers on a hand are used. These fingers are codes as p-pinkie, r-ringfinger, m-middle finger, i-index finger, and t-thumb. A number of posesfor the fingers and thumbs are defined and illustrated in FIG. 3. Agesture vocabulary string establishes a single character position foreach expressible degree of freedom in the of the linkage (in this case,a finger). Further, each such degree of freedom is understood to bediscretized (or ‘quantized’), so that its full range of motion can beexpressed through assignment of one of a finite number of standard ASCIIcharacters at that string position. These degrees of freedom areexpressed with respect to a body-specific origin and coordinate system(the back of the hand, the center of the grasshopper's body; the base ofthe robotic arm; etc.). A small number of additional gesture vocabularycharacter positions are therefore used to express the position andorientation of the linkage ‘as a whole’ in the more global coordinatesystem.

Still referring to FIG. 3, a number of poses are defined and identifiedusing ASCII characters. Some of the poses are divided between thumb andnon-thumb. The invention in this embodiment uses a coding such that theASCII character itself is suggestive of the pose. However, any charactermay used to represent a pose, whether suggestive or not. In addition,there is no requirement in the invention to use ASCII characters for thenotation strings. Any suitable symbol, numeral, or other representationmaybe used without departing from the scope and spirit of the invention.For example, the notation may use two bits per finger if desired or someother number of bits as desired.

A curled finger is represented by the character “ˆ” while a curled thumbby “>”. A straight finger or thumb pointing up is indicated by “1” andat an angle by “\” or “/”. “−” represents a thumb pointing straightsideways and “x” represents a thumb pointing into the plane.

Using these individual finger and thumb descriptions, a robust number ofhand poses can be defined and written using the scheme of the invention.Each pose is represented by five characters with the order beingp-r-m-i-t as described above. FIG. 3 illustrates a number of poses and afew are described here by way of illustration and example. The hand heldflat and parallel to the ground is represented by “11111”. A fist isrepresented by “{circumflex over ( )}>”. An “OK” sign is represented by“111ˆ>”.

The character strings provide the opportunity for straightforward ‘humanreadability’ when using suggestive characters. The set of possiblecharacters that describe each degree of freedom may generally be chosenwith an eye to quick recognition and evident analogy. For example, avertical bar (‘|’) would likely mean that a linkage element is‘straight’, an ell (‘L’) might mean a ninety-degree bend, and acircumflex (‘ˆ’) could indicate a sharp bend. As noted above, anycharacters or coding may be used as desired.

Any system employing gesture vocabulary strings such as described hereinenjoys the benefit of the high computational efficiency of stringcomparison—identification of or search for any specified pose literallybecomes a ‘string compare’ (e.g. UNIX's ‘strcmp( )’ function) betweenthe desired pose string and the instantaneous actual string.Furthermore, the use of ‘wildcard characters’ provides the programmer orsystem designer with additional familiar efficiency and efficacy:degrees of freedom whose instantaneous state is irrelevant for a matchmay be specified as an interrogation point (‘?’); additional wildcardmeanings may be assigned.

Orientation

In addition to the pose of the fingers and thumb, the orientation of thehand can represent information. Characters describing global-spaceorientations can also be chosen transparently: the characters ‘<’, ‘>’,‘ˆ’, and ‘v’ may be used to indicate, when encountered in an orientationcharacter position, the ideas of left, right, up, and down. FIG. 4illustrates hand orientation descriptors and examples of coding thatcombines pose and orientation. In an embodiment of the invention, twocharacter positions specify first the direction of the palm and then thedirection of the fingers (if they were straight, irrespective of thefingers' actual bends). The possible characters for these two positionsexpress a ‘body-centric’ notion of orientation: ‘−’, ‘+’, ‘x’, ‘*’, ‘ˆ’,and ‘v’ describe medial, lateral, anterior (forward, away from body),posterior (backward, away from body), cranial (upward), and caudal(downward).

In the notation scheme of and embodiment of the invention, the fivefinger pose indicating characters are followed by a colon and then twoorientation characters to define a complete command pose. In oneembodiment, a start position is referred to as an “xyz” pose where thethumb is pointing straight up, the index finger is pointing forward andthe middle finger is perpendicular to the index finger, pointing to theleft when the pose is made with the right hand. This is represented bythe string “{circumflex over ( )}x1−:−x”.

‘XYZ-hand’ is a technique for exploiting the geometry of the human handto allow full six-degree-of-freedom navigation of visually presentedthree-dimensional structure. Although the technique depends only on thebulk translation and rotation of the operator's hand—so that its fingersmay in principal be held in any pose desired—the present embodimentprefers a static configuration in which the index finger points awayfrom the body; the thumb points toward the ceiling; and the middlefinger points left-right. The three fingers thus describe (roughly, butwith clearly evident intent) the three mutually orthogonal axes of athree-space coordinate system: thus ‘XYZ-hand’.

XYZ-hand navigation then proceeds with the hand, fingers in a pose asdescribed above, held before the operator's body at a predetermined‘neutral location’. Access to the three translational and threerotational degrees of freedom of a three-space object (or camera) iseffected in the following natural way: left-right movement of the hand(with respect to the body's natural coordinate system) results inmovement along the computational context's x-axis; up-down movement ofthe hand results in movement along the controlled context's y-axis; andforward-back hand movement (toward/away from the operator's body)results in z-axis motion within the context. Similarly, rotation of theoperator's hand about the index finger leads to a ‘roll’ change of thecomputational context's orientation; ‘pitch’ and ‘yaw’ changes areeffected analogously, through rotation of the operator's hand about themiddle finger and thumb, respectively.

Note that while ‘computational context’ is used here to refer to theentity being controlled by the XYZ-hand method—and seems to suggesteither a synthetic three-space object or camera—it should be understoodthat the technique is equally useful for controlling the various degreesof freedom of real-world objects: the pan/tilt/roll controls of a videoor motion picture camera equipped with appropriate rotational actuators,for example. Further, the physical degrees of freedom afforded by theXYZ-hand posture may be somewhat less literally mapped even in a virtualdomain: In the present embodiment, the XYZ-hand is also used to providenavigational access to large panoramic display images, so thatleft-right and up-down motions of the operator's hand lead to theexpected left-right or up-down ‘panning’ about the image, butforward-back motion of the operator's hand maps to ‘zooming’ control.

In every case, coupling between the motion of the hand and the inducedcomputational translation/rotation may be either direct (i.e. apositional or rotational offset of the operator's hand maps one-to-one,via some linear or nonlinear function, to a positional or rotationaloffset of the object or camera in the computational context) or indirect(i.e. positional or rotational offset of the operator's hand mapsone-to-one, via some linear or nonlinear function, to a first orhigher-degree derivative of position/orientation in the computationalcontext; ongoing integration then effects a non-static change in thecomputational context's actual zero-order position/orientation). Thislatter means of control is analogous to use of a an automobile's ‘gaspedal’, in which a constant offset of the pedal leads, more or less, toa constant vehicle speed.

The ‘neutral location’ that serves as the real-world XYZ-hand's localsix-degree-of-freedom coordinate origin may be established (1) as anabsolute position and orientation in space (relative, say, to theenclosing room); (2) as a fixed position and orientation relative to theoperator herself (e.g. eight inches in front of the body, ten inchesbelow the chin, and laterally in line with the shoulder plane),irrespective of the overall position and ‘heading’ of the operator; or(3) interactively, through deliberate secondary action of the operator(using, for example, a gestural command enacted by the operator's‘other’ hand, said command indicating that the XYZ-hand's presentposition and orientation should henceforth be used as the translationaland rotational origin).

It is further convenient to provide a ‘detent’ region (or ‘dead zone’)about the XYZ-hand's neutral location, such that movements within thisvolume do not map to movements in the controlled context.

Other poses may included:

[|||||:vx] is a flat hand (thumb parallel to fingers) with palm facingdown and fingers forward.

[|||||:xˆ] is a flat hand with palm facing forward and fingers towardceiling

[|||||:−x] is a flat hand with palm facing toward the center of the body(right if left hand, left if right hand) and fingers forward

[{circumflex over ( )}−:−x] is a single-hand thumbs-up (with thumbpointing toward ceiling)

[{circumflex over ( )}|−:−x] is a mime gun pointing forward

Two Hand Combination

The present invention contemplates single hand commands and poses, aswell as two-handed commands and poses. FIG. 5 illustrates examples oftwo hand combinations and associated notation in an embodiment of theinvention. Reviewing the notation of the first example, “full stop”reveals that it comprises two closed fists. The “snapshot” example hasthe thumb and index finger of each hand extended, thumbs pointing towardeach other, defining a goal post shaped frame. The “rudder and throttlestart position” is fingers and thumbs pointing up palms facing thescreen.

Orientation Blends

FIG. 6 illustrates an example of an orientation blend in an embodimentof the invention. In the example shown the blend is represented byenclosing pairs of orientation notations in parentheses after the fingerpose string. For example, the first command shows finger positions ofall pointing straight. The first pair of orientation commands wouldresult in the palms being flat toward the display and the second pairhas the hands rotating to a 45 degree pitch toward the screen. Althoughpairs of blends are shown in this example, any number of blends arecontemplated in the invention.

Example Commands

FIG. 8 illustrates a number of possible commands that may be used withthe present invention. Although some of the discussion here has beenabout controlling a cursor on a display, the invention is not limited tothat activity. In fact, the invention has great application inmanipulating any and all data and portions of data on a screen, as wellas the state of the display. For example, the commands may be used totake the place of video controls during play back of video media. Thecommands may be used to pause, fast forward, rewind, and the like. Inaddition, commands may be implemented to zoom in or zoom out of animage, to change the orientation of an image, to pan in any direction,and the like. The invention may also be used in lieu of menu commandssuch as open, close, save, and the like. In other words, any commands oractivity that can be imagined can be implemented with hand gestures.

Operation

FIG. 7 is a flow diagram illustrating the operation of the invention inone embodiment. At step 701 the detection system detects the markers andtags. At decision block 702 it is determined if the tags and markers aredetected. If not, the system returns to step 701. If the tags andmarkers are detected at step 702, the system proceeds to step 703. Atstep 703 the system identifies the hand, fingers and pose from thedetected tags and markers. At steps 704 the system identifies theorientation of the pose. At step 705 the system identifies the threedimensional spatial location of the hand or hands that are detected.(Please note that any or all of steps 703, 704, and 705 may be combinedas a single step).

At step 706 the information is translated to the gesture notationdescribed above. At decision block 707 it is determined if the pose isvalid. This may be accomplished via a simple string comparison using thegenerated notation string. If the pose is not valid, the system returnsto step 701. If the pose is valid, the system sends the notation andposition information to the computer at step 708. At step 709 thecomputer determines the appropriate action to take in response to thegesture and updates the display accordingly at step 710.

In one embodiment of the invention, steps 701-705 are accomplished bythe on-camera processor. In other embodiments, the processing can beaccomplished by the system computer if desired.

Parsing and Translation

The system is able to “parse” and “translate” a stream of low-levelgestures recovered by an underlying system, and turn those parsed andtranslated gestures into a stream of command or event data that can beused to control a broad range of computer applications and systems.These techniques and algorithms may be embodied in a system consistingof computer code that provides both an engine implementing thesetechniques and a platform for building computer applications that makeuse of the engine's capabilities.

One embodiment is focused on enabling rich gestural use of human handsin computer interfaces, but is also able to recognize gestures made byother body parts (including, but not limited to arms, torso, legs andthe head), as well as non-hand physical tools of various kinds, bothstatic and articulating, including but not limited to calipers,compasses, flexible curve approximators, and pointing devices of variousshapes. The markers and tags may be applied to items and tools that maybe carried and used by the operator as desired.

The system described here incorporates a number of innovations that makeit possible to build gestural systems that are rich in the range ofgestures that can be recognized and acted upon, while at the same timeproviding for easy integration into applications.

The gestural parsing and translation system in one embodiment consistsof:

1) a compact and efficient way to specify (encode for use in computerprograms) gestures at several different levels of aggregation:

-   -   a. a single hand's “pose” (the configuration and orientation of        the parts of the hand relative to one another) a single hand's        orientation and position in three-dimensional space    -   b. two-handed combinations, for either hand taking into account        pose, position or both    -   c. multi-person combinations; the system can track more than two        hands, and so more than one person can cooperatively (or        competitively, in the case of game applications) control the        target system    -   d. sequential gestures in which poses are combined in a series;        we call these “animating” gestures    -   e. “grapheme” gestures, in which the operator traces shapes in        space

2) a programmatic technique for registering specific gestures from eachcategory above that are relevant to a given application context

3) algorithms for parsing the gesture stream so that registered gesturescan be identified and events encapsulating those gestures can bedelivered to relevant application contexts

The specification system (1), with constituent elements (1a) to (1f),provides the basis for making use of the gestural parsing andtranslating capabilities of the system described here.

A single-hand “pose” is represented as a string of

i) relative orientations between the fingers and the back of the hand,

ii) quantized into a small number of discrete states.

Using relative joint orientations allows the system described here toavoid problems associated with differing hand sizes and geometries. No“operator calibration” is required with this system. In addition,specifying poses as a string or collection of relative orientationsallows more complex gesture specifications to be easily created bycombining pose representations with further filters and specifications.

Using a small number of discrete states for pose specification makes itpossible to specify poses compactly as well as to ensure accurate poserecognition using a variety of underlying tracking technologies (forexample, passive optical tracking using cameras, active optical trackingusing lighted dots and cameras, electromagnetic field tracking, etc).

Gestures in every category (1a) to (1f) may be partially (or minimally)specified, so that non-critical data is ignored. For example, a gesturein which the position of two fingers is definitive, and other fingerpositions are unimportant, may be represented by a single specificationin which the operative positions of the two relevant fingers is givenand, within the same string, “wild cards” or generic “ignore these”indicators are listed for the other fingers.

All of the innovations described here for gesture recognition, includingbut not limited to the multi-layered specification technique, use ofrelative orientations, quantization of data, and allowance for partialor minimal specification at every level, generalize beyond specificationof hand gestures to specification of gestures using other body parts and“manufactured” tools and objects.

The programmatic techniques for “registering gestures” (2), consist of adefined set of Application Programming Interface calls that allow aprogrammer to define which gestures the engine should make available toother parts of the running system.

These API routines may be used at application set-up time, creating astatic interface definition that is used throughout the lifetime of therunning application. They may also be used during the course of the run,allowing the interface characteristics to change on the fly. Thisreal-time alteration of the interface makes it possible to

i) build complex contextual and conditional control states,

ii) to dynamically add hysterisis to the control environment, and

iii) to create applications in which the user is able to alter or extendthe interface vocabulary of the running system itself.

Algorithms for parsing the gesture stream (3) compare gestures specifiedas in (1) and registered as in (2) against incoming low-level gesturedata. When a match for a registered gesture is recognized, event datarepresenting the matched gesture is delivered up the stack to runningapplications.

Efficient real-time matching is desired in the design of this system,and specified gestures are treated as a tree of possibilities that areprocessed as quickly as possible.

In addition, the primitive comparison operators used internally torecognize specified gestures are also exposed for the applicationsprogrammer to use, so that further comparison (flexible state inspectionin complex or compound gestures, for example) can happen even fromwithin application contexts.

Recognition “locking” semantics are an innovation of the systemdescribed here. These semantics are implied by the registration API (2)(and, to a lesser extent, embedded within the specification vocabulary(1)). Registration API calls include

i) “entry” state notifiers and “continuation” state notifiers, and

ii) gesture priority specifiers.

If a gesture has been recognized, its “continuation” conditions takeprecedence over all “entry” conditions for gestures of the same or lowerpriorities. This distinction between entry and continuation states addssignificantly to perceived system usability.

The system described here includes algorithms for robust operation inthe face of real-world data error and uncertainty. Data from low-leveltracking systems may be incomplete (for a variety of reasons, includingocclusion of markers in optical tracking, network drop-out or processinglag, etc).

Missing data is marked by the parsing system, and interpolated intoeither “last known” or “most likely” states, depending on the amount andcontext of the missing data.

If data about a particular gesture component (for example, theorientation of a particular joint) is missing, but the “last known”state of that particular component can be analyzed as physicallypossible, the system uses this last known state in its real-timematching.

Conversely, if the last known state is analyzed as physicallyimpossible, the system falls back to a “best guess range” for thecomponent, and uses this synthetic data in its real-time matching.

The specification and parsing systems described here have been carefullydesigned to support “handedness agnosticism,” so that for multi-handgestures either hand is permitted to satisfy pose requirements.

Coincident Virtual/Display and Physical Spaces

The system can provide an environment in which virtual space depicted onone or more display devices (“screens”) is treated as coincident withthe physical space inhabited by the operator or operators of the system.An embodiment of such an environment is described here. This currentembodiment includes three projector-driven screens at fixed locations,is driven by a single desktop computer, and is controlled using thegestural vocabulary and interface system described herein. Note,however, that any number of screens are supported by the techniquesbeing described; that those screens may be mobile (rather than fixed);that the screens may be driven by many independent computerssimultaneously; and that the overall system can be controlled by anyinput device or technique.

The interface system described in this disclosure should have a means ofdetermining the dimensions, orientations and positions of screens inphysical space. Given this information, the system is able todynamically map the physical space in which these screens are located(and which the operators of the system inhabit) as a projection into thevirtual space of computer applications running on the system. As part ofthis automatic mapping, the system also translates the scale, angles,depth, dimensions and other spatial characteristics of the two spaces ina variety of ways, according to the needs of the applications that arehosted by the system.

This continuous translation between physical and virtual space makespossible the consistent and pervasive use of a number of interfacetechniques that are difficult to achieve on existing applicationplatforms or that must be implemented piece-meal for each applicationrunning on existing platforms. These techniques include (but are notlimited to):

1) Use of “literal pointing”—using the hands in a gestural interfaceenvironment, or using physical pointing tools or devices—as a pervasiveand natural interface technique.

2) Automatic compensation for movement or repositioning of screens.

3) Graphics rendering that changes depending on operator position, forexample simulating parallax shifts to enhance depth perception.

4) Inclusion of physical objects in on-screen display—taking intoaccount real-world position, orientation, state, etc. For example, anoperator standing in front of a large, opaque screen, could see bothapplications graphics and a representation of the true position of ascale model that is behind the screen (and is, perhaps, moving orchanging orientation).

It is important to note that literal pointing is different from theabstract pointing used in mouse-based windowing interfaces and mostother contemporary systems. In those systems, the operator must learn tomanage a translation between a virtual pointer and a physical pointingdevice, and must map between the two cognitively.

By contrast, in the systems described in this disclosure, there is nodifference between virtual and physical space (except that virtual spaceis more amenable to mathematical manipulation), either from anapplication or user perspective, so there is no cognitive translationrequired of the operator.

The closest analogy for the literal pointing provided by the embodimentdescribed here is the touch-sensitive screen (as found, for example, onmany ATM machines). A touch-sensitive screen provides a one to onemapping between the two-dimensional display space on the screen and thetwo-dimensional input space of the screen surface. In an analogousfashion, the systems described here provide a flexible mapping(possibly, but not necessarily, one to one) between a virtual spacedisplayed on one or more screens and the physical space inhabited by theoperator. Despite the usefulness of the analogy, it is worthunderstanding that the extension of this “mapping approach” to threedimensions, an arbritrarialy large architectural environment, andmultiple screens is non-trivial.

In addition to the components described herein, the system may alsoimplement algorithms implementing a continuous, systems-level mapping(perhaps modified by rotation, translation, scaling or other geometricaltransformations) between the physical space of the environment and thedisplay space on each screen.

A rendering stack which takes the computational objects and the mappingand outputs a graphical representation of the virtual space.

An input events processing stack which takes event data from a controlsystem (in the current embodiment both gestural and pointing data fromthe system and mouse input) and maps spatial data from input events tocoordinates in virtual space. Translated events are then delivered torunning applications.

A “glue layer” allowing the system to host applications running acrossseveral computers on a local area network.

Thus, a gesture based control system has been described.

1. A method of controlling a computer display comprising: detecting aphysical control gesture made by a user; translating the control gestureto an executable command; updating the computer display in response tothe executable command.